1. Field of the Invention
The present invention relates to a pylon for an aircraft, i.e. a structure that fixes a turbomachine to an aircraft fuselage. More specifically, the invention relates to a device internal to the pylon allowing both a reduction in the noise created by the pylon and a cooling of the turbomachine.
2. Description of the Related Art
FIG. 1 shows an aircraft equipped with two propellers 9 of the type known as “propfan”. The propfan propellers comprise a turbomachine each housed in a nacelle 7 fixed by support struts 1, also known as pylons, to a fuselage 8 of the aircraft.
The turbomachine of a propfan propeller comprises two counter-rotating rotors each comprising a set of equidistant blades 92a, 92b, and positioned in the rear part of the propeller.
The pylon is an aerodynamic fairing that surrounds the structure supporting the turbomachine and, amongst others, allows the fuel, electrical, hydraulic, and air systems to be routed between the turbomachine and the aircraft.
Although it has an aerodynamic profile, the pylon causes vortices in its wake when the aircraft is in flight.
The vortices cause a variation in total pressure on the rotor blades, generating noise and vibration phenomena due to the interaction between the blades and the vortices.
Various solutions have been developed to reduce these phenomena.
To reduce the area subjected to the vortices and therefore reduce the noise induced by the pylon, it is known to blow pressurized air from the pylon into the vortices of said pylon's wake.
One can cite, amongst others, U.S. Pat. No. 5,156,353, which describes an example of an aircraft pylon comprising a slot at a trailing edge of the pylon allowing pressurized air to be blown into the vortices.
Generally, the blowing of air is achieved by collecting air at the turbomachine's compressors. This therefore represents an impact on the propulsive efficiency of the turbomachine.
Moreover, the turbomachine generates significant heat dissipation, mainly by mechanical friction, through its lubricating fluid.
It is clear that this heat must be dissipated to the outside environment to cool the engine.
Equipment mounted on the turbomachine, such as an electric generator, may also require cooling.
Various solutions have been developed to perform this cooling.
A first known solution, mainly for turbofan-type propellers, consists of installing a heat exchanger, called a volumetric heat exchanger, between an outer wall and an inner wall of the nacelle. An air inlet collects cold air from the cold air flow going through the turbomachine, to bring it inside said volumetric heat exchanger. After passing through the heat exchanger matrix, the air is ejected out of the nacelle through an air outlet. Such heat exchangers have not proved to be an optimal solution in terms of propulsive efficiency and of aerodynamic impact on the turbomachine. In effect, the air collection represents a direct loss of propulsive efficiency inasmuch as it contributes little or nothing to the engine's thrust. Moreover, the presence of an air inlet, one or more internal ducts and an air outlet generates load losses and disturbs the propeller's internal flow more or less significantly.
Another known solution consists of using an exchanger, called a surface exchanger, such as for example a plate heat exchanger. In particular a surface exchanger is known that locally takes the form of an inner wall of the nacelle or of an engine cover to which it is coupled. A first surface of the surface exchanger is coupled to the inner wall of the nacelle or to the engine cover, while a second surface is located in the flow of cold air flowing through the internal volume of the nacelle. The heat transported within the heat exchanger is transferred by thermal conduction to the inner surface of the plate forming the second surface of the plate heat exchanger. This hot plate is traversed by the flow of cold air flowing in the nacelle. The heat stored in the hot plate on the inner surface is thus dissipated by forced convection towards the propeller's airflow.
This solution still has an aerodynamic impact, but has the advantage, compared to the previous solution, of not collecting air from the flow through the turbomachine.
However, this solution cannot be transposed to propfan-type propellers. Indeed, when the aircraft speed is low or zero, there is little or no air flow traversing the surface exchanger, because the rotors are arranged outside the nacelle.